1. Field of the Invention
The present invention relates to a wireless local area network (WLAN), and more specifically to an apparatus and method for managing power save mode in a WLAN system.
2. Related Art
Advances in a wireless local access network (WLAN) make mobile phone users, such as Laptop computer users, easy to perform their works due to an improved mobility. For example, users can carry with their laptop computers to a meeting room in order to attend a conference, and can get on a local network through WLAN.
For a system based on Institute of Electrical and Electronics Engineers (IEEE) 802.11 standards, Basic Service Set (BSS) refers to a station assembly that is successfully synchronized. And a Basic Service Area (BSA) refers to an area including members that consist of BSS. BSA may be changed according to characteristics of radio wave in a wireless media. BSS may be basically classified into two configurations, an independent BSS and an infrastructured BSS (IBSS). The former implies BSS that establishes a self-contained network and cannot access to a Distribution System (DS), and the latter implies BSS that includes one or more a Access Point (AP), the Distribution System (DS), and the like and generally use AP in all of the communication processes including the communications between the stations.
According to IEEE 802.11e standard “Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications/Amendment 8: Medium Access Control (MAC) Quality of Service Enhancements” published at Nov. 11, 2005, it was not allow to directly transmit data between non-AP STAs in the IBSS, but it surely required through a AP in order to the data transmissions. It means that the station in BSS cannot directly transmit data to other STA, and pass through AP in order to frame transmission.
Further, since TREE 802.11e standard, a Direct link Setup (DLS) between non-AP STAs is having supported. The station can directly transmit the frame to other station through DLS Direct link
The station is operated in two power management modes, such as one of an Active Mode (AM) and a Power Save Mode (PSM). The station in the AM keeps in the awake state, and the station in the PSM transitions between the wakeup state and a doze state. The station is awake at the beginning of the wakeup state and stays awake during a wake window. The station in the wakeup state can transmit and/or receive frames. The station in the doze state cannot transmit and/or receive frames.
Generally, the station belongs to user as a portable device, so that supporting PSM is essential to effectively manage a power. In the IEEE 802.11e standard, the management of the power is called an Automatic Power Save Deliver (APSD). APSD has two mechanisms: an unscheduled APSD (U-APSD) and a scheduled APSD (S-APSD).
The management of the power is needed for the direct link. According to IEEE 802.11e, after DLS Direct link is setup, the station in AM or PSM transmits a DATA Frame and/or a Management Frame to other station through DLS Direct link.
In order to establishing DLS direct link, a DLS Request Frame and a DLS Response Frame between two non-AP STAs are exchanged through AP. It means that AP supporting IEEE 802.11e is required in order for the setup of the DLS direct link. However, since WLAN system that has been used widely is based only on the IEEE 802.11a/b/g standards, the AP supporting the IEEE 802.11a/b/g cannot support DLS. Therefore, even though non-AP STAs supports IEEE 802.11e, non-AP STAs cannot setup DLS direct link through the AP, so that DLS service cannot be utilized.
A Tunneled Direct link Setup (TDLS) has been introduced in order to establish a direct link between non-AP STAs even if the AP cannot support IEEE 802.11e. In the TDLS, TDLS direct link is set up through encapsulated data frames.
There is a need for a technique for effectively managing the PSM under the TDLS direct link